Various sensors have been used to monitor water quality. Currently available water quality sensor technology is based generally on adaptations, modifications, and extensions of conventional analytical chemistry equipment and techniques. Some examples follow.
U.S. Pat. No. 5,965,882 issued on Oct. 12, 1999 to Megerle et al. describes a miniaturized ion mobility spectrometer sensor cell that comprised an improved spectrometer for detecting chemical warfare agents and hazardous vapors.
U.S. Pat. No. 5,922,183 issued on Jul. 13, 1999 to Rauh describes a metal oxide matrix. Thin film composites of the oxides and biological molecules such as enzymes, antibodies, antigens and DNA strands can be used for both amperometric and potentiometric sensing.
U.S. Pat. No. 5,866,430 issued on Feb. 2, 1999 to Grow describes a methodology and devices for detecting or monitoring or identifying chemical or microbial analytes. The described methodology comprises four basic steps: (1) The gas or liquid medium to be monitored or analyzed is brought into contact with a bioconcentrator which is used to bind with or collect and concentrate one or more analytes. (2) The bioconcentrator-analyte complex is then exposed to radiation of one or more predetermined wavelengths to produce Raman scattering spectral bands. (3) At least a portion of the Raman spectral bands is collected and processed by a Raman spectrometer to convert the same into an electrical signal. And (4) the electrical signal is processed to detect and identify, qualitatively and/or quantitatively, the analyte(s).
U.S. SIR No. H1344 issued on Aug. 2, 1994 to Baldauf et al describes a portable automatic sensor for toxic gases. Their method provided for the integration of a low-volume liquid flow and sampling system and a portable optical waveguide-based fluorescence detector for the chemical analysis of reagents in fluorescence-based reactions. In a preferred embodiment, the presence and concentration of acetylcholinesterase inhibitors, such as chemical warfare nerve agents or certain insecticides, is determined by mixing aqueous samples with a dilute solution of n-methyl indoxyl acetate, and monitoring the formation of a fluorescent product (n-methyl indoxyl).
U.S. Pat. No. 4,906,440 issued on Mar. 6, 1990 to Kolesar describes a sensor for detecting chemicals. In this sensor a gas detector is described that detects the presences of the gas when the gas reacts with a distributed RC notch network to cause a shift in operating frequency and notch depth. A metallic/metallic oxide gas sensitive discontinuous film acts as the distributive resistive element in the RC notch network. The gas changes the conductivity of the film and this causes the network to react. In the preferred embodiment, a copper/cuprous oxide film detects organophosphorus compounds, which can be chemical warfare agents.
U.S. Pat. No. 4,752,226 issued on Jun. 21, 1988 to Akers et al. describes a method for simulating chemical warfare attack that includes the use of a radiant energy transmitting device for radiating energy in a pattern which simulates different types and forms of chemical agents. Protective devices, such as gas masks, protective clothing, or structures, are provided with sensors for determining whether the protective device is properly employed.
U.S. SIR No. H454 issued on Apr. 5, 1988 to Sickenberger, et al. describes a method of detecting leaks within artillery shells, bombs and other munitions which involves the permanent in situ insertion within the munitions cavity of an electrically resistive surface which varies in resistance with the adsorption of leaking chemical vapors. In a typical embodiment of the invention, the electrically resistive surface is serially connected with an identical surface with an inert coating and the voltage drops across both the coated and uncoated surfaces are measured.
It is well-known that there is a close correlation between photosynthetic activity and fluorescence from plants. The following scientific and technical publications are recommended for a basic understanding of the technology:
1. Krause, G. H. and Weis, E., (1991) Chlorophyll fluorescence and photosynthesis: the basics, Annu. Rev. Plant Physiol. Plant Mol. Biol. 42: 313-349.
2. Krause, G. H., Vernotte, C., and Briantais, J.-M., (1982) Photoinduced quenching of chlorophyll fluorescence in intact chloroplasts and algae. Biochimica et Biophysica Acta. 679: 116-124.
3. Schreiber, U., Bilger, W., and Neubauer, C., (1994) Chlorophyll fluorescence as a nonintrusive indicator for rapid assessment of in vivo photosynthesis. Ecological Studies 100: 49-70.
4. Genty, B., Briantais, J.-M., and Baker, N. R., (1989) The relationship between the quantum yield of photosynthetic electron transport and quenching of chlorophyll fluorescence. Biochimica et Biophysica Acta. 990:87-92.
5. Van Kooten and Snel (1990) tabulated the use of chlorophyll fluorescence nomenclature in plant stress physiology.
6. Edwards, G. E. and Baker, N. R., (1993) Can CO2 assimilation in maize leaves by predicted accurately from chlorophyll fluorescence analysis? Photo. Res. 37: 89-102.
7. Seaton, G. G. R. and Walker, D. A., (1995) Chlorophyll fluorescence as a measure of photosynthetic carbon assimilation. Proc. R. Soc. London Ser. B. 242: 99-108.
8. Naessens, M., Leclerc J. C., Tran-Minh, C. 2000. Fiber optic biosensor using Chlorella vulgaris for determination of toxic compounds. Ecotoxicol. Environ. Saf., 46, 181-185.
Naessens et al. have reported a fiber optic biosensor using entrapped Chlorella vulgaris for determination of toxic compounds in water. Naessens et al. uses filter paper-entrapped Chlorella and flows a water sample through the filter-paper. The entrapped algae are an integral part of the instrument. A disadvantage of a system using entrapped algae is that fouling of the sensor is a serious problem since the instrument is useless after such fouling until a new sensor is installed. This is not practical for remote, continuous monitoring.
A treatise on chemical warfare agents may also be helpful. See, for example, Satu M. Sonami, Chemical Warfare Agents Academic Press, 1992.